[04/11] media: i2c: imx290: Fix the pixel rate at 148.5Mpix/s

  The datasheet lists the link frequency changes between
1080p and 720p modes. This is correct that the link frequency
changes as measured on an oscilloscope.

Link frequency is not necessarily the same as pixel rate.

The datasheet gives standard configurations for 1080p and 720p
modes at a number of frame rates.
Looking at the 1080p mode it gives:
HMAX = 0x898 = 2200
VMAX = 0x465 = 1125
2200 * 1125 * 60fps = 148.5MPix/s

Looking at the 720p mode it gives:
HMAX = 0xce4 = 3300
VMAX = 0x2ee = 750
3300 * 750 * 60fps = 148.5Mpix/s

This driver currently scales the pixel rate proportionally to the
link frequency, however the above shows that this is not the
correct thing to do, and currently all frame rate and exposure
calculations give incorrect results.

Correctly report the pixel rate as being 148.5MPix/s under any
mode.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
---
 drivers/media/i2c/imx290.c | 15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)
  

Hi Dave,

Thank you for the patch.

On Tue, Jan 31, 2023 at 07:20:09PM +0000, Dave Stevenson wrote:
> The datasheet lists the link frequency changes between
> 1080p and 720p modes. This is correct that the link frequency
> changes as measured on an oscilloscope.
> 
> Link frequency is not necessarily the same as pixel rate.

That's right. The model where

	htotal * vtotal * frame rate = pixel rate

applies to the pixel array. Things can be retimed when transmitted over
CSI-2 (or over anything, really), with pixels transmitted at a higher or
lower rate, with smaller or larger blanking, as long as it matches the
total horizontal line length in time units. I suppose this could in
theory be done vertically too, but that would require too much memory.

I hope we'll never have a need, on the receiver side, to know the active
line length in time units as sent over CSI-2 :-)

> The datasheet gives standard configurations for 1080p and 720p
> modes at a number of frame rates.
> Looking at the 1080p mode it gives:
> HMAX = 0x898 = 2200
> VMAX = 0x465 = 1125
> 2200 * 1125 * 60fps = 148.5MPix/s
> 
> Looking at the 720p mode it gives:
> HMAX = 0xce4 = 3300
> VMAX = 0x2ee = 750
> 3300 * 750 * 60fps = 148.5Mpix/s
> 
> This driver currently scales the pixel rate proportionally to the
> link frequency, however the above shows that this is not the
> correct thing to do, and currently all frame rate and exposure
> calculations give incorrect results.
> 
> Correctly report the pixel rate as being 148.5MPix/s under any
> mode.
> 
> Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
> ---
>  drivers/media/i2c/imx290.c | 15 ++++-----------
>  1 file changed, 4 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/media/i2c/imx290.c b/drivers/media/i2c/imx290.c
> index 12946ca9d8d2..bd8729aed43c 100644
> --- a/drivers/media/i2c/imx290.c
> +++ b/drivers/media/i2c/imx290.c
> @@ -107,6 +107,7 @@
>  
>  #define IMX290_VMAX_DEFAULT				1125
>  
> +#define IMX290_PIXEL_RATE				148500000

A blank line is missing here. With this fixed,

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

>  /*
>   * The IMX290 pixel array is organized as follows:
>   *
> @@ -190,7 +191,6 @@ struct imx290 {
>  
>  	struct v4l2_ctrl_handler ctrls;
>  	struct v4l2_ctrl *link_freq;
> -	struct v4l2_ctrl *pixel_rate;
>  	struct v4l2_ctrl *hblank;
>  	struct v4l2_ctrl *vblank;
>  };
> @@ -649,15 +649,8 @@ static void imx290_ctrl_update(struct imx290 *imx290,
>  {
>  	unsigned int hblank = mode->hmax - mode->width;
>  	unsigned int vblank = IMX290_VMAX_DEFAULT - mode->height;
> -	s64 link_freq = imx290_link_freqs_ptr(imx290)[mode->link_freq_index];
> -	u64 pixel_rate;
> -
> -	/* pixel rate = link_freq * 2 * nr_of_lanes / bits_per_sample */
> -	pixel_rate = link_freq * 2 * imx290->nlanes;
> -	do_div(pixel_rate, imx290_format_info(format->code)->bpp);
>  
>  	__v4l2_ctrl_s_ctrl(imx290->link_freq, mode->link_freq_index);
> -	__v4l2_ctrl_s_ctrl_int64(imx290->pixel_rate, pixel_rate);
>  
>  	__v4l2_ctrl_modify_range(imx290->hblank, hblank, hblank, 1, hblank);
>  	__v4l2_ctrl_modify_range(imx290->vblank, vblank, vblank, 1, vblank);
> @@ -707,9 +700,9 @@ static int imx290_ctrl_init(struct imx290 *imx290)
>  	if (imx290->link_freq)
>  		imx290->link_freq->flags |= V4L2_CTRL_FLAG_READ_ONLY;
>  
> -	imx290->pixel_rate = v4l2_ctrl_new_std(&imx290->ctrls, &imx290_ctrl_ops,
> -					       V4L2_CID_PIXEL_RATE,
> -					       1, INT_MAX, 1, 1);
> +	v4l2_ctrl_new_std(&imx290->ctrls, &imx290_ctrl_ops, V4L2_CID_PIXEL_RATE,
> +			  IMX290_PIXEL_RATE, IMX290_PIXEL_RATE, 1,
> +			  IMX290_PIXEL_RATE);
>  
>  	v4l2_ctrl_new_std_menu_items(&imx290->ctrls, &imx290_ctrl_ops,
>  				     V4L2_CID_TEST_PATTERN,